Volume Regulation

Question 1

What is the nephron?

Answer 1

the fundamental functional unit of the kidney

Question 2

Why is the effective circulating volume measured instead of the extracellular water content?

Answer 2

Because the body can’t easily measure the total extracellular water content

Question 3

What is the juxtaglomerular apparatus?

Answer 3

the complex of late distal tubule in association with renal afferent arteriole

Question 4

What is the macula densa?

Answer 4

the thickening of the wall of the early distal tubule

Question 5

What is the aim of the renin-angiotensin-aldosterone system?

Answer 5

to increase the effective circulating volume

Question 6

What happens when there is a low Na+ conc in the distal tubule?

Answer 6

look at diagram on lecture

Question 7

What are the effects of producing angiotensin II?

Answer 7

• efferent arteriole vasoconstriction (increase in hydrostatic pressure, increase in filtration rate) keeps GF in nephron
• increase Na+ reabsorption in proximal tube (causes water reabsorption increasing volume without changing osmolality)
• can cause aldosterone release from adrenal cortex which increases Na+ reabsorption by distal tubule and collecting duct ( same as earlier mechanism)

Question 8

What are the two main physiological triggers for aldosterone release?

Answer 8

ATII

hyperkalaemia

Question 9

What is the other role of aldosterone?

Answer 9

control of K+ secretion

Question 10

What does spironolactone block?

Answer 10

effect of aldosterone

Question 11

Where does spironolactone act?

Answer 11

in the collecting tubules and ducts

Question 12

What are the uses of spironolactone?

Answer 12

heart failure (K+ sparing diuretic)

Question 13

What 4 locations in the renin angiotensin system can be used to control blood pressure?

Answer 13

• ACE inhibitors
• AT1 receptor antagonists
• Aldosterone receptor antagonists
• renin inhibition

Question 14

What is the main receptor for angiotension II?

Answer 14

AT1 receptor

Question 15

What are the effects of angiotensin II?

Answer 15

1. vasoconstriction
2. increase Na+/H+ exchange in the proximal tubule. and hence proximal Na+ and water reabsorption
3. increase in aldosterone release from the adrenal cortex, which increases distal Na+ absorption
4. causes ADH release
5. Causes thirst

Question 16

What are the effects of activating sympathetic innervation of afferent arteriole?

Answer 16

1. the vasocontriction upstream of granule cells causes a further fall in the pressure sensed by these cells and hence amplifies the fall in wall pressure, generated by a fall in blood pressure
2. direct stimulation of renin release from the granule cells
3. afferent arteriole vasoconstriction drops glomerular hydrostatic pressure to the glomerulus and hence lowers GFR